The present invention relates to an information recording medium, and more particularly to a format of a recording area thereof.
Many optical recording and reproducing apparatus which use recording media such as optical files or compact disks have recently been proposed, and card-like optical recording media (optical cards) which are superior in point of the ease of carrying and of their large memory capacity have also been proposed.
FIG. 1A shows a plan view of a recording format of a prior art optical card and FIG. 1B shows a partial enlarged view thereof. A recording area 2 is provided on an optical card 1 which is a recording medium and has a plurality of bands 3 arranged therein. Each of the bands 3 has a number of tracks (4600 tracks in the illustrated embodiment) arranged therein and each track 4 has an information capacity of several tens to 100 bits (46 bits in the illustrated embodiment). As shown in FIG. 1B, each track 4 comprises a start bit 20, a stop bit 21, a track number field 22 and a data field 23 (including a parity bit for error correction). One track comprises 46 bits of which 5 bits are used for the track number area.
The bands are separated by reference lines (R lines) 5, and a home position HP which is an access reference position is formed at a corner of the optical card. An arrow A indicates a direction of movement of the optical card 1 in a reproduction mode.
FIG. 2 shows a configuration of an optical card reproducing apparatus. The optical card 1 is movable in the direction of the arrow A by means of a rotation mechanism 6. Information recorded on the optical card 1 is read and reproduced by an optical head 11 track by track. A light beam from a light source 7 such as an LED is condensed by a lens system 8 to illuminate the track 4 on which the information is recorded. An image of the illuminated track 4 is focused by a focusing optical system 9 on a linear array sensor 10 which produces an electrical signal representing the information recorded on the track 4.
In order to access a desired track on the optical card 1, the optical head 11 is moved in a direction of an arrow C (see FIG. 1A) with the home position HP being a reference position. Theoptical head 11 selects the band 3 to which the desired track belongs by counting the R lines 5 and stops at the desired band. Then, the optical card 1 is moved by the rotation mechanism 6 in the direction of the arrow A, and the information on the desired track is read.
When the track number field 22 comprises 5 bits, only 32 combinations are possible and all of the 4600 tracks in one band cannot be selected. In order to select the 4600 tracks, 13 bits are required for the track number field but they occupy a large portion of total of 46 bits. Thus, redundancy is high. Further, as the number of bits in the track number field 22 increases, the probability of misdetection of the track number due to dust or defect increases accordingly.
The correct detection of the track number is very important because it is a basic requirement for reproduction. In a recording medium like the optical card in which the number of bits in one track cannot be very large, it is very important to reduce the redundancy to increase the data capacity.